1. Field of the Invention
The present invention relates to a semiconductor device having a display portion for displaying information such as images and characters. More particularly, the present invention relates to a structure of a driver circuit for transmitting a signal to each pixels in a pixel region that constitutes a display portion, to a method of manufacturing the same, and to a mounting method thereof. Also, the present invention relates to a semiconductor device having a region in which thin film transistors are arranged in matrix, and in particular, to a circuit structure, its manufacturing method and its mounting method, which is formed separately with the above matrix circuit. Note that, throughout this specification, a semiconductor device denotes a general device that can function by utilizing semiconductor characteristics and that the category of semiconductor devices includes electronic equipment.
2. Description of the Related Art
In display devices provided with a liquid crystal layer or a light-emitting layer, an active matrix display, in which thin film transistors (TFTs) are arranged in matrix to form the pixel region, is known as means for forming a screen for displaying an image etc. Representative example thereof is an active matrix liquid crystal display device, and is used for various types of electronic equipment such as a notebook type personal computer (note PC), a mobile computer, a portable telephone, and a liquid crystal television, which is propagating widely. Compared to a CRT, it is possible to make this type of display device lighter weight and thinner, and depending upon its use, there is a demand for giving the screen a large surface area and increasing the density of pixels.
Techniques of forming a channel-forming region of TFT by using an amorphous semiconductor film, typically amorphous silicon, have superior productivity. The amorphous semiconductor film has the characteristic of being able to be formed on a relatively low cost, large surface area substrate, such as barium borosilicate glass and aluminum borosilicate glass. However, the largest value of the electric field effect mobility that can be obtained in a TFT in which the channel forming region is formed from the amorphous silicon film, is only on the order of 1 cm2/Vsec. The TFT can therefore be used as a switching TFT (a pixel TFT) to be formed in the pixel region, but cannot be used for forming a driver circuit to drive it. Consequently, the driver circuit for the pixel TFT uses an IC chip manufactured on a single crystal silicon substrate, and is mounted in the periphery of the pixel region by a TAB (tape automated bonding) method or a COG (chip on glass) method.
The TAB method is a method of mounting an IC chip, in which a wiring is formed on a flexible insulating substrate using such as copper foil, and the IC chip is mounted directly thereon. Further, one edge of the flexible substrate is connected to an input terminal of the display device. On the other hand, the COG method is a method of sticking the IC chip directly onto a wiring pattern along its pattern, which is formed on the substrate of the display device, thereby being connected.
Also, the techniques of mounting the driver circuit on the substrate of the display device, as disclosed in Japanese Patent Application Laid-open Nos. Hei 7-014880 and Hei 11-160734, in which a driver circuit is formed from a TFT, manufactured by a non-single crystal semiconductor material on a substrate such as glass or quartz, and partitioned into strips (such substrates having a driver circuit cut into a strip shape are hereafter referred to as stick drivers), have been disclosed as other methods of mounting the driver circuit.
Whichever method is used, it is preferable to make the region in which the driver circuit is mounted as small as possible on the substrate on which the pixel region is formed, and various designs have been ingeniously made for the method of driver circuit mounting, including the wiring layout.
In such display devices, if the number of pixels increases, then the number of IC chips to be mounted thereon will also inevitably become large. In an RGB full color display XGA panel, the number of terminals on the data line side of the pixel region alone becomes approximately 3000, further, 4800 are necessary for UXGA. The size of the IC chip is limited by the wafer size in the manufacturing process, and the practical size limit of the longer side is on the order of 20 mm. In this IC chip, the pitch of the output terminals depends on a method of forming contact by plating, and is generally 50 to 200 im, and 50 to 80 im if the pitch is made minute, which is said as a limit thereof. Even a pitch of 50 μm is attained, one IC chip can only cover 400 connection terminals. Approximately 8 IC chips are required on only the data line side in the above XGA panel, and 12 IC chips are necessary for the UXGA panel.
A method of manufacturing a long size IC chip has also been considered, but the number of strip shape IC chips which can be cut out from a circular shape silicon wafer is naturally lowered, and therefore the method is not practical. In addition, the silicon wafer itself has a fragile nature, and if a rather long IC chip is manufactured, then the probability of breakage increases. Also, the mounting of the IC chips requires precise placement of the same and reduction in contact resistance of the terminal portion. If the number of IC chips joined to one panel increases, then the probability of defects developing increases, which leads to a fear of reducing the yield in that process. In addition, the temperature coefficient of the silicon which becomes the substrate of the IC chip differs from the temperature coefficient of the glass substrate on which the pixel region is formed, and therefore problems such as warping develop after the two substrates are joined. This becomes a cause of a lowering in the reliability of the element due to the developed mechanical stress, as well as of direct defects such as an increase in the contact resistance.
On the other hand, it is possible to form the driver circuit with a length equal to that of the pixel region by using the stick driver, and also possible to form the driver with one stick driver to be mounted. However, if an area of surface of the circuit portion increases, the number of stick drivers which become defective due to a single point defect increases, and therefore the number which can be cut out of one substrate is reduced, causing a reduction in the process yield.
From the viewpoint of productivity, a method of forming a plurality of stick drivers from TFTs manufactured from a crystalline semiconductor film on a large surface area glass substrate or quartz substrate is considered superior. However, the driving frequency differs between the scanning line side and the data line side, and further, the value of the driving voltage applied also differs. Specifically, the TFTs in the stick driver of the scanning line side must withstand on the order of 30 V, while the driving frequency is equal to or less than 100 KHz, and therefore no high speed operationability is required. A voltage resistance on the order of 12 V is sufficient for the TFTs in the stick driver of the data line side, but high speed operation is required such that a driving frequency at 3 V is on the order of 65 MHz. Thus, it is necessary to make the structure of the stick driver and the TFTs within the drivers different in accordance with the different specifications to be required.